(1) Field of the Invention
The present invention relates generally to a method for treating or preventing systemic inflammation.
(2) Description of the Related Art
The inflammatory response is an attempt by the body to restore and maintain homeostasis after invasion by an infectious agent, antigen challenge, or physical, chemical or traumatic damage. Localized inflammation is contained in a specific region and can exhibit varying symptoms, including redness, swelling, heat and pain.
While the inflammatory response is generally considered a healthy response to injury, the immune system can present an undesirable physiological response if it is not appropriately regulated. In this situation, the body's normally protective immune system causes damage to its own tissue by treating healthy tissue as if it is infected or abnormal. Alternatively, if there is an injury, the inflammatory response may be out of proportion with the threat causing the injury. When this occurs, the inflammatory response can cause more damage to the body than the agent itself would have produced.
The inflammatory response has been found in part to consist of an increased expression of both pro-inflammatory and anti-inflammatory cytokines. Cytokines are low molecular weight, biologically active proteins involved in the coordination of immunological and inflammatory responses and communication between specific immune cell populations. A number of cell types produce cytokines during inflammatory reactions, including neutrophils, monocytes, and lymphocytes.
Multiple mechanisms exist by which cytokines generated at inflammatory sites influence the inflammatory response. If a pro-inflammatory response is not successfully countered by anti-inflammatory cytokines, however, uncontrolled systemic inflammation can occur.
In contrast to localized inflammation, systemic inflammation is widespread throughout the body. This type of inflammation may include localized inflammation at specific sites, but may also be associated with general “flu-like” symptoms, including fever, chills, fatigue or loss of energy, headaches, loss of appetite, and muscle stiffness. Systemic inflammation can lead to protein degradation, catabolism and hypermetabolism. As a consequence, the structure and function of essential organs, such as muscle, heart, immune system and liver may be compromised and can contribute to multi-organ failure and mortality. Jeschke, et al., Insulin Attenuates the Systemic Inflammatory Response to Thermal Trauma, Mol. Med. 8(8):443-450 (2002). Although enormous progress has been achieved in understanding the mechanisms of systemic inflammation, the mortality rate due to this disorder remains unacceptably high.
Often, whether the cytokine response is pro- or anti-inflammatory depends on the balance of individual microorganisms that colonize the intestinal lumen at any particular time. It is well known that the mucosal surface of the intestinal tract is colonized by an enormously large, complex, and dynamic collection of microorganisms. The composition of the intestinal microflora varies along the digestive tract as well as in different micro-habitats, such as the epithelial mucus layer, the deep mucus layer of the crypts, and the surface of mucosal epithelial cells. The specific colonization depends on external and internal factors, including luminally available molecules, mucus quality, and host-microbial and microbial-microbial interactions. Murch, S. H., Toll of Allergy Reduced by Probiotics, Lancet, 357:1057-1059 (2001).
These microorganisms, which make up the gut microflora, are actively involved with the immune response. They interact with the epithelium in conditions of mutual beneficial relationships for both partners (symbiosis) or in conditions of benefit for one partner, without being detrimental to the other (commensalisms). Hooper, et al., How Host-Microbial Interactions Shape the Nutrient Environment of the Mammalian Intestine, Annu. Rev. Nutr. 22:283-307 (2002) In fact, considerable evidence is emerging which shows a strong interplay or “cross-talk” between the intestinal microflora and the diverse population of cells in the intestinal mucosa. Bourlioux, et al., The Intestine and its Microflora are Partners for the Protection of the Host: Report on the Dan one Symposium “The Intelligent Intestine” held in Paris, Jun. 14, 2002, Am. J. Clin. Nutr. 78:675 (2003); Hooper, L. V. & Gordon, J. I., Commensal Host-Bacterial Relationships in the Gut, Sci. 292:1115 (2001); Haller, et al., Non-Pathogenic Bacteria Elicit a Differential Cytokine Response by Intestinal Epithelial Celt/Leucocyte Co-Cultures, GUT 47:79 (2000); Walker, W. A., Role of Nutrients and Bacterial Colonization in the Development of Intestinal Host Defense, J. Pediatr. Gastroenterol. Nutr. 30:S2 (2000). Additionally, the gut microflora has been shown to elicit specific immune responses at both a local and systemic level in adults. Isolauri, E., et al., Probiotics: Effects on Immunity, Am. J. Clin. Nutr. 73:444S-50S (2001).
The gut microflora in infants is known to be far less developed than that of an adult. While the microflora of the adult human consists of more than 1013 microorganisms and nearly 500 species, some being harmful and some being beneficial, the microflora of an infant contains only a fraction of those microorganisms, both in absolute number but also species diversity. Infants are born with a sterile gut, but acquire intestinal flora from the birth canal, their initial environment, and what they ingest. Because the gut microflora population is very unstable in early neonatal life, it is often difficult for the infant's gut to maintain the delicate balance between harmful and beneficial bacteria, thus reducing the ability of the immune system to function normally.
It is especially difficult for formula-fed infants to maintain this balance due to the differences between the bacterial species in the gut of a formula-fed and breast-fed infant. The stool of breast-fed infants contains predominantly Bifidobacterium, with Streptococcus and Lactobacillus as less common contributors. In contrast, the microflora of formula-fed infants is more diverse, containing Bifidobacterium and Bacteroides as well as the more pathogenic species, Staphylococcus, Escherichia coli, and Clostridia. The varied species of Bifidobacterium in the stools of breast-fed and formula-fed infants differ as well. A variety of factors have been proposed as the cause for the different fecal flora of breast-fed and formula-fed infants, including the lower content and different composition of proteins in human milk, a lower phosphorus content in human milk, the large variety of oligosaccharides in human milk, and numerous humoral and cellular mediators of immunologic function in breast milk. Agostoni, et al., Probiotic Bacteria in Dietetic Products for Infants. A Commentary by the ESPGHAN Committee on Nutrition, J. Pediatr. Gastro. Nutr. 38:365-374 (April 2004).
Because the microflora of formula-fed infants is so unstable and the gut microflora largely participate in stimulation of gut immunity, formula-fed infants are more likely to develop inflammatory illnesses. Many of the major illnesses that affect infants, including chronic lung disease, periventricular leukomalacia, neonatal meningitis, neonatal hepatitis, sepsis, and necrotizing enterocolitis are inflammatory in nature. Depending on the particular disease, the accompanying inflammation can occur in a specific organ, such as the lung, brain, liver or intestine, or the inflammation can truly be systemic in nature.
For example, chronic lung disease causes the tissues inside the lungs to become inflamed while neonatal meningitis involves inflammation of the linings of the brain and spinal cord. Periventricular leukomalacia is caused by inflammatory damage to the periventricular area in the developing brain. Necrotizing enterocolitis causes inflammation in the intestine that may result in destruction of part or all of the intestine and neonatal hepatitis involves an inflammation of the liver that occurs in early infancy. Sepsis, also known as systemic inflammatory response syndrome, is a severe illness caused by an overwhelming infection of the bloodstream by toxin-producing bacteria. In this disease, pathogens in the bloodstream elicit an inflammatory response throughout the entire body.
Premature and critically ill infants also represent a serious challenge in terms of developing gut immunity and preventing systemic inflammation. Preterm or critically ill infants are often placed immediately into sterile incubators, where they remain unexposed to the bacterial populations to which a healthy, term infant would normally be exposed. This may delay or impair the natural colonization process. These infants are also often treated with broad-spectrum antibiotics, which kill commensal bacteria that attempt to colonize the infant's intestinal tract. Additionally, these infants are often nourished by means of an infant formula, rather than mother's milk. Each of these factors may cause the infant's gut microflora to develop improperly, thus causing or precipitating life-threatening systemic inflammation.
In recent years, the supplementation of probiotic bacteria into the diet of formula-fed infants has been suggested in order to encourage gut colonization with beneficial microorganisms. Probiotic bacteria are living microorganisms that exert beneficial effects on the health of the host. Fuller, R. Probiotics in Man and Animals, J. Appl. Bacteriol. 66: 365-78 (1989).
While viable probiotic bacteria may be effective in normalizing the gut microflora, there have been very few published studies assessing their safety in premature and immunosuppressed infants. These special populations have an immature gut defense barrier that increases the risk for translocation of luminal bacteria, causing a potentially heightened risk for infections. In many cases, viable probiotics are not recommended for immunosuppressed patients, post cardiac surgery patients, patients with pancreatic dysfunction, or patients with blood in the stool. At least one death has been reported due to probiotic supplementation in an immunosuppressed individual. MacGregor G., et al. Yoghurt biotherapy: contraindicated in immunosuppressed patients? Postgrad Med J. 78: 366-367 (2002).
Thus, for immunosuppressed patients or premature infants, it would be useful to provide a non-viable supplement that may treat or prevent systemic inflammation. A non-viable alternative to live probiotics may have additional benefits such as a longer shelf-life. Live probiotics are sensitive to heat, moisture, and light, and ideally should be refrigerated to maintain viability. Even with these precautions, the shelf-life of a typical probiotic is relatively short. A non-viable alternative to live probiotics would circumvent the necessity of refrigeration and would provide a product having a longer shelf-life. The product could then be distributed to regions of the world without readily available refrigeration. A non-viable alternative to probiotics would additionally provide less risk of interaction with other food components, such as fermentation and changes in the taste, texture, and freshness of the product. Accordingly, it would be beneficial to provide a method for reducing or preventing systemic inflammation in formula-fed infants comprising the administration of inactivated probiotics.